Top 3 formal-proofs open source projects

A proof-producing SMT/McSat solver, handling polymorphic first-order logic, and using an SMT/McSat core extended using Tableaux, Superposition and Rewriting.

A Coq library providing tactics to deal with hypothesis

Variations on Kirby & Paris' hydra battles and other entertaining math in Coq (collaborative, documented, includes exercises) [maintainer=@Casteran]